Differential pressure gauge



A 27,1937. T. H. RISK DIFFERENTIAL PRESSURE GAUGE Filed Nov. 27, 1934 2 Sheets-Sheet 1 gay 7 22 Patented Apr. 27, 1937 UNITED STATES PATENT OFFICE DIFFERENTIAL PRESSURE GAUGE Application November 2'1, 1934, Serial No. 754,949

' 3 Claims.

This invention relates to instruments of the class wherein differences in pressures are made use of to obtain indications or measurements.

The apparatus of my invention is particularly adapted to be used in indicating apparatus of the type where the difference between pressures on opposite sides of an orifice through which fluid is flowing is made use of to indicate the rate of flow therethrough, or in which the difference between static and dynamic pressures of a flowing fluid is made use of to indicate the rate of flow thereof. I have found that it is particularly adapted, for instance, to the measurement of the rate of consumption of fuel in an aeroplane, or to the measurement of the speed of an aeroplane relative to the air, or for the measurement of the rate of flow of fluid in a pipe, or for any similar measurement. I

Some of the diiiiculties encountered with prior art instruments of this type are delicacy, and

inability to operate in any and all positions. Another difficulty has arisen from imposing the different pressures upon opposite sides of a single diaphragm, leakage of which would seriously im- 26 pair the accuracy without becoming evident to the observer. Many such instruments have failed of accuracy because of excessive backlash and lost motion in connective linkages, or because of dependence upon delicate springs to transmit accurate readings. Other difficulties have arisen because of inherent construction which necessitated widely diiferent degrees of scale accuracy at different points in the range. Many of these difficulties '1 have avoided by my novel construction.

Certain objects of this invention are to provide an instrument of this class having a minimum of operative parts, rugged, capable of sustained accuracy under severe conditionsjof service, having a minimum number of operative linkages which may permit back-lash and looseness, having a scale of reasonably comparable accuracy throughout its range, and such other objects and advantages as may be later set forth. In order that my invention may be fully understood, attention is directed to the drawings showing its several parts, which drawings are attached to and hereby made a part of this specification. In the drawings, Figure 1 is an elevation of the instrument, partially in section, and Figure 2 is another elevation, 90 degrees removed from that of Figure 1. Figure 3 is a section of a modified form, corresponding'to Figure l, and Figure 4 an elevation of the modified form, corresponding to Figure 2,

Referring now to the drawings, and reading Figures 1 and 2 together, 5 denotes a cylindrical casing, composed of three parts, 6, l, and 8, held together by a series of through bolts denoted by numerals 9. When assembled, with dia- 5 phragms, these parts constitute a pair of pressure chambers l0 and II, each composed of one of the end sections and a diaphragm' l2, and an intervening neutral chamber, open to the atmosphere. The two diaphragms l2 are operatively connected together in a neutral position by connecting link l3, having in its middle a'stirrup l4. Vertically mounted in the neutral chamber is an operating lever l5, the middle portion of which is a leaf spring, which middle portion passes through the stirrup l4. Contact between this lever I5 and the sides of the stirrup i4 is so maintained that the lateral displacement of connecting link l3 results in a corresponding displacement of lever Hi. The bottom end of lever I5 is fixed by cooperation of the two lever pivot bearing pins I6 and the lever spring tension ad justing screw ll. When a difference in pressure between chambers l0 and H exists, the position of the diaphragms I2 is changed, resulting in lateral motion of connecting link l3. This lateral motion of I3 transmitted through stirrup M to lever l5 results in a movement of the upper end of lever l5 through an are described about the center of flexure of spring lever 15. A rack arm 30 I8 is'pin mounted on the upper end of lever arm l5, and held by means of; spring l9 in contact with a pinion 20. Movement of the end of lever l5 thus effects rotative motion of the pinion 20 and pointer shaft 2|, which is supported by 30 needle bearings 22 mounted in suitable supports 23 which are fixed on the instrument body 5. A

' pointer 2Q is affixed to the pointer shaft 2|, and

travels over a dial 25 supported by one of the supports 23. Pressure chambers I0 and II are supplied with pressure connections 26 and air bleed connections 21 which may be suitably piped in the customary manner. In order that proper zero adjustments may be made, an adjusting Wedge 28 is provided, with a rider 29 for contact with lever 15. Adjusting wedge 28 is positioned by thumbscrew 30. The adjusting wedge 28 consists of a conical enlargement of the shaft of the thumbscrew 30, so that when the screw is turned the wedge 28 advances or recedes across the 50 lever I5. The rider 29 may be formed most con-' veniently as a projection from lever l5, having an inclined plane face for contact with conical wedge 28. This zero adjustment provides a stop means ior'lever i5, and through it establishes position of the diaphragm mecha 'stru'ction instead of the leaf spring lever l5 of Figures 1 and 2, I make use of a rigid lever, designated I5A, which swings about a center provided by needle bearing pin 3|. A socket 32 is provided at the fixed end of lever I5A, and torsion spring bar 33 is firmly aifixed therein. This torsion spring bar 33 is concentric with bearing pin 3| and extends without casing 5 through openin 34. An external support 35 affixed to casing 5 is provided, and clamp 36 with set screws 31 .and 38 serves to fix the outboard end of bar 33.

This form of construction has the merit of providing a fixed fulcrum for lever ISA, and a more rugged form of spring resistance. Additionally, the clamp 36 may be varied in position to afiord a longer or shorter active length of torsion spring bar 33, thus securing an easy adjustment of spring strength and any desired pointer travel for various pressure differentials. This renders the adjustment of the instrument for use in various pressure ranges quite easy and convenient.

Some of the advantages flowing from this novel construction by means of which the objects of this invention are attained are pointed out in the following discussion.

Each diaphragm is in contact on one side with actuating fluid and on the other with the atmosphere, and a leak or break in a diaphragm is at once signalled by escape of fluid. There are a minimum of operative parts, and likewise a minimum of points where wear may. impair accuracy. The operative parts employed are simple and rugged in construction. No dependence is placed upon the maintenance of strength of any delicate spring. Positive mechanical contact is depended upon for the transmission of indications. v

With small differential pressures a small motion of the diaphragms occurs, and small motion of the spring lever arm is had.- With large differences of pressure, large motions of the dia- Dhragms would be had, except that they are limited by the increasing resistance .ofthe spring lever arm l5. These two forces, working oppositely, tend to cause a similar rotation of the pointer shaft for similar increments of differential pressure at all points in the range of the scale, and proportions and spring strength may be so chosen or adjusted that scale divisions are practically constant throughout the operative range. This is the sole point where any dependence is made upon the continued strength of a spring. The spring here used is rugged, and in addition a quick and eifective means of stiffening the spring is furnished by means of the spring.

lever tension screw II, or by the torsion bar 33. When more rugged construction is desired, at the sacrifice of some accuracy at the extremities of the range, a mere lever may be substituted for the spring lever here described.

Further, the mechanism here shown is not of a' type subject to derangement by vibrations. Similarly it has no part depending upon gravity for its action, and may be mounted in any position', or may be subjected without loss of accuracy I have found this device a be punctual-151 adapted for use, in an aeroplane in connection with a Venturi tube to show. the rate of gasoline consumption. In this use, I may insert a Yen'- to change of position turi nozzle or tube at some convenient point in the fuel flow line, and may connect one of the pressure chambers to the low pressure zone of said Venturi tube and the other to the high pressure zone. The pressure, lead tubes should be brought from the Venturi tube to the differential pressure gauge in such a manner that they are at all times equidistant from a plane passed through'the horizontal axes of the wings and fuselage. Before reading the gauge, the air in the pressure lead tubes and diaphragm cham hers is bled out by opening the pet-cocks or other valvesplaced in the vent openings It, to insure that the fuel fills both the pressure leads and the instrument chambers. With the flow meter tube, tubing, and gauge mounted as described, and without air or other gases in the pressure measuring system, no maneuver of the airplane except those involving slipping or skidding will cause an err r due to differences in static head, and the instru ent will read correctly in allother maneuvers. Since such conditions of flight which would cause errors are met with during only relatively short times, the essential accuracy of the instrument for the intended purpose is not im paired.

Various modifications may be made in this invention without departing from the spirit and scope thereof as set forth in the following claims.

I claim:

1. In an instrument for the measurement of differential pressures, a casing, and mounted therein two pressure responsive diaphragms dividing said casing into a low pressure chamber, a high pressure chamber, and therebetween a neutral chamber open to the atmosphere, each diaphragm being the sole pressure responsive member of the chamber of which it is a part, between said diaphragms and connected thereto a link member of fixed length adapted to be moved laterally by the differential movement of the diaphragms, a spring lever, means for fixing one end thereof, anoperative connection between said spring lever and said diaphragm link member, whereby lateral movement of said link member causes proportional deflection of the free end of said spring lever, upon theiree end of said spring lever a rack, a pinion'and pinion shaft operated thereby, a pointer aflixed to said pinion shaft,'and

a dial overwhieh said pointer may travel.

2. In an instrument for the measurement of differential pressures, a casing, and mounted therein two pressure responsive diaphragms dividing said easing into a low pressure chamber, a high-pressure chamber, and therebetweenna neutral chamber open to the atmosphere, each member of the chamber of which it is a part,

between said diaphragms'and connected thereto pinion shaftadapted tov contact with said rack and to be rotated by movement thereof, a spring acting between the spring lever and therack bar to force said rack bar into operative contact with said pinion, a pointer aflixed to the pinion shaft, and a dialover which said pointer may travel.

3. In an ,instrument for the measurement of diaphragm being the sole pressure responsive differential pressures, a casing, and mounted therein two pressure responsive diaphragms dividing said easing into a low pressure chamber, a high pressure chamber, and therebetween a neutral chamber open to the atmosphere, each dia-. phragm being the sole pressure responsive member of the chamber of which it is a part, between said diaphragms and connected thereto a link member of fixed length adapted to be moved laterally 10 by the differential movement of the diaphragms, a

lever, a fixed fulcrum point for said'lever, a torsion spring bar of variable effective lengthaflix'ed to said lever and acting to vary the resistance of said lever to motion, an operative connection be- I tween said lever and said diaphragm link member,

whereby lateral movement of said link member causes proportional deflection of the free end of said lever, upon the free end of said lever a rack, a pinion and pinion shaft operated thereby, a pointer aflixed to said pinion shaft, and a dial over which said pointer may travel.

' THOMAS H. RISK. 

